J Orofac Pain 30 (2016), No. 1 27. Jan. 2016
J Orofac Pain 30 (2016), No. 1 (27.01.2016)
Upregulation of the Purinergic Receptor Subtype P2X3 in the Trigeminal Ganglion Is Involved in Orofacial Pain Induced by Occlusal Interference in Rats
Qi, Dong / Yang, Yingying / Ji, Ping / Kong, Jingjing / Wu, Qingting / Si, Huiling
Aims: To evaluate whether the purinergic receptor subtype P2X3 (P2X3R) in trigeminal ganglion (TG) neurons is involved in hyperalgesia of the temporomandibular joints (TMJs) and masseter muscles associated with placement of an occlusal interference.
Methods: Forty-five rats were randomized into five groups (ie, for days 1, 3, 7, 14, or 28; nine rats per group). Six rats from each group were chosen to receive the occlusal interference, and the remaining three rats were sham-treated controls. On days 1, 3, 7, 14, and 28 after placement of the occlusal interference, the mechanical pain threshold (MPT) to stimulation of the TMJs or masseter muscles was examined using von Frey filaments. Seven days after the occlusal interference placement, changes in MPT were tested after administration of the P2X3R antagonist A-317491 into the TMJs and masseter muscles (60 μg/site) in six rats. The expression of P2X3R in the TGs was investigated by immunohistochemistry and quantitative polymerase chain reaction (qPCR). Retrograde tracing was combined with immunofluorescence to identify TMJ and masseter muscle afferent neurons in the TGs of six premature rats.
Results: The TMJ and masseter muscle MPTs were decreased after placement of the occlusal interference, and the P2X3R antagonist reversed the mechanical hyperalgesia that was caused by the occlusal interference placement. The frequency of P2X3R-immunoreactive cells increased in small-sized neurons in the TG after occlusal interference. By contrast, there was no increase in medium-sized TG neurons. P2X3R mRNA increased on day 3. Retrograde tracing indicated that the TMJ and masseter muscle afferent neurons in the TG expressed P2X3R.
Conclusion: Upregulated P2X3R expression in the TG may contribute to orofacial pain development induced by an occlusal interference. P2X3R may be a therapeutic target for chronic TMJ or masseter muscle pain.
Keywords: masseter muscle, occlusal interference, orofacial hyperalgesia, P2X3 receptor, temporomandibular joint